As used herein, “/” denotes alternative names for the same or similar components or structures. That is, a “/” can be taken as meaning “or” as used herein. Unicast transmissions are between a single sender/transmitter and a single receiver. Broadcast transmissions are between a single sender/transmitter and all receivers within receiving range of the transmitter. Multicast transmissions are between a single sender/transmitter and a subset of the receivers within receiving range of the transmitter where the subset of receivers with receiving range of the transmitter may be the entire set. That is, multicast may include broadcast and is therefore a broader term than broadcast as used herein. Data/content is transmitted in packets or frames. As used herein a station can be a node or a client device, which can be a mobile terminal or mobile device such as, but not limited to, a computer, laptop, personal digital assistant (PDA) or dual mode smart phone. Specifically, a wireless device may be a mobile device but a wireless device may also be fixed and not moving for a particular period of time.
Recently there has been a rapid and significant increase of wireless network deployment on school and work campuses, in shopping malls, at libraries, airports, at homes, etc. Emerging technologies such as IEEE 802.11n make delivering multimedia content over wireless links possible. Thus, the technology is being driven deeper into our daily lives. The number of interference free channels is limited. In a dense deployment environment, wireless networks tend to interfere with each other. This interference impacts the throughput of wireless networks and thus, the quality of service for multimedia streaming applications. The present invention is directed to channel assignment methods and apparatus that will optimize the channel usage, promote channel reuse and improve the throughput as well as quality of service for multimedia applications.
A great deal of work has been done regarding channel assignment in cellular networks. The infrastructure of a cellular network is, however, quite different from that of an IEEE 802.11 wireless local area network. In a cellular network, each base station may have one or more channels. Through careful channel planning by the operator to avoid interference, neighboring base stations will not share the same channel. An IEEE 802.11 wireless local area network may include one or more basic service sets (BSS). Each BSS includes an access point (AP) and the clients that are associated with the AP. Each BSS is assigned one channel. The AP and the clients share the same channel using carrier sense multiple access/collision avoidance (CSMA/CA) MAC layer protocol. In fact, based on CSMA/CA, two or more neighboring BSSs may share the same channel if the sum of the load of each BSSs is less than the channel capacity.
Channel assignment has also been studied extensively in multihop wireless networks such as wireless mesh and ad hoc networks. Existing multihop wireless networks often use off-the-shelf IEEE 802.11 MAC layer protocol products and algorithms. Data or content may need to be transmitted over multiple wireless hops before reaching a destination. Conventional channel assignment algorithms in multihop wireless networks often assume a mobile device in the network has two or more wireless interfaces, and conventional channel assignment algorithms are further constrained by issues such as routing efficiency and connectivity of the network. These algorithms do not work well for densely deployed wireless local area networks operating in the infrastructure mode.
Conventional channel assignment methods for WLANs adopt a static, one-time channel assignment approach. A network administrator conducts a site survey and layout planning, and then manually assign channels to APs such that the assignments experience minimum interference. This approach does not adapt well to a dynamic environment. Recent proposals have focused on automatic channel assignment. In one such proposal, the least congested channel selection (LCCS) algorithm, the AP periodically scans the channels and selects the least congested channel. LCCS is AP-centric in nature. It does not detect any client side conflicts. In another recent proposal, a client-driven approach for channel assignments targeted conventional WLANs and is not suitable for WLANs that are designed specifically for multimedia applications where there are strict constraints on the demand and bit rate for each client. In another recent proposal, the demand at each demand point needs to be explicitly specified, and channels are assigned to APs such that channel usage is maximized. However, in the problem formulation, it was assumed that interference between APs was symmetric, and neighboring APs were assigned to interference free channels. This is not necessarily true in practical deployments, as neighboring APs may have different power levels and thus different interference ranges, so the interference may not be symmetric. Also if the total demand on neighboring APs is lower than the channel capacity, neighboring APs can be assigned the same channel. In yet another recent proposal, a traffic aware channel assignment method was introduced. However, this model also assumed symmetric interference and did not address the hidden and exposed terminal problem.
IEEE 802.11h has defined dynamic frequency selection (DFS). DFS selects a channel for a mobile device to avoid interference with radar and/or satellite signals, and is not designed to improve the over all performance of a wireless network in a dense deployment environment.